Lining wear indicators

ABSTRACT

A brake lining wear indicator comprises a preferably normally closed switch. The switch can be operated by feelers in a disc brake or the switch can be incorporated in a tie. The normally closed switches are connected in series to a relay preferably having a delayed action.

[ 1 June 19, 1973 [56] References Cited UNITED STATES PATENTS LININGWEAR INDICATORS [75] Inventor: Charles Newstead, Walsall, England 340/52F 340/52 A Fiorita et a]. 200/61 4 Veilleux.................;..........

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[21] Appl' l55700 Primary Examiner-Robert K. Schaefer AssistantExaminer-M. Ginsburg [30] Foreign Application Priority DataAttorneyScrivener, Parker, Scrivener & Clarke ABSTRACT A brake liningwear indicator comprises a preferably normally closed switch. The switchcan be operated by 00 777 470 09 152 34 mnm iii am BBB mmm eee rrr GGG00 1 W 1 .0 6 21 et nPn u a .JSJ

feelers in a disc brake or the switch can be incorporated in a tie. Thenormally closed switches are connected in series to a relay preferablyhaving a delayed action.

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Patented June 19, 1973 8 Sheets-Sheet 5 Patented June 19, 1973 8Sheets-Sheet 6 Ill 2.- .I r s Patented June 19, 1973 3,740,566

8 Sheets-Sheet 7 LINING WEAR INDICATORS The present invention relates tobrake lining wear indicators.

The object of the present invention is to provide a vehicle brake liningwear indication system in which each brake has at least one reusablewear indicator having at least a pair of contacts which are normallyspringbiassed together and in which the contacts are arranged in aseries circuit which operates a means such that a break in the seriescircuit causes an indication.

Embodiments of the invention will now be described, by way of examplewith reference to the accompanying drawings.

FIG. 1 is a face view on a drum brake showing locations A, B, C, D, Eand F where lining wear indicators can have their ends attached,

FIG. 2 is a face view on a lining wear indicator,

FIG. 3 is a side view taken in the direction of arrow III of FIG. 2,

FIG. 4 is an enlarged cross-sectional view of an electrical switch shownin FIGS. 2 and 3,

' FIG. 5 is a face view showing an alternative construction to thatillustrated in FIG. 2 but with the right hand side of theindicatorrotated through a right angle, the figure being shown insection,

FIG. 6 is an electrical circuit showing a plurality of indicatorswitches connected in series,

FIG. 7, a side view of an actuating mechanism ofa disc brake omittingfor simplicity anti-rattle springs and retaining clips,

FIG. 8, a detail section on line VIII-VIII of FIG. 7,

FIG. 9, a plan view on the actuating mechanism of FIG. 7,

FIG. 10, a section in plan on an enlarged scale of a limit switch usedin the actuation mechanism of FIG. 7,

FIG. 11 is another circuit diagram,and

FIG. 12 is another circuit diagram.

DETAILED DESCRIPTION OF THE EMBODIMENTS FIG. 1 is a face view on a drumbrake of which a brief description will begiven. Two arcuate frictionassemblies llare carried from a torque or backing plate 12 and aremovable relative thereto by an actuator 13 and an adjustor 14. Thefriction assemblies each consists of a carrier 15- and at least onefrictional shoe, lining or pad 10 integrally attached thereto. Thesefrictional assemblies are pulled together away from a drum (not shown)by'pull-off springs 16. The invention is applicable to most, if not all,types of drum brakes and no benefit is to be gained by amplifying thisdescription of a drum brake.

The only modifications to the standard components of a drum brakeentailed by the present invention, are the provision of a hole 17 forelectrical leads (or like signal transmitting provision) in the torqueor backing plate 12, attachment points such as holes or studs 18 in oron the carriers 15, and the optional fitting of .a wear indicator 19(FIG. 2). The provision of holes 17 and holes or studs 18 is veryinexpensive and can be incorporated at little cost in standardproduction runs.

Depending on the information required, the wear indicator can be fittedbetween a number of positions. For detecting the need for adjustment asuitable position is between A and C but if one brake lining is likelyto wear faster it may be preferred to fit the indicator between a fixedposition on the backing plate such as position B and either or both ofpositions A and C. With sliding shoe brakes, the position B should be onthe perpendicular line to the sliding face passing through therespective position A or C. There may be separate positions B forindicators connected to positions A or C. For detecting the need forbrake shoe replacement positions D and F are suitable or position E withone or both of positions D and F. A plurality of indicators can befitted to a single brake and connected in series to indicate a singlefault or in parallel to indicate total failure.

With some types of adjustor it may be possible to isolate the indicatorfrom the amount of adjustment by connecting the indicator between a partof the adjustor or something that moves with adjustment of the adjustorand the brake shoe; this is particularly convenient with a brake usingan adjustor acting between the shoe and tappet.

The wear indicator 19 is a separate fitting which can be secured betweentwo carriers by suitable means such as bolts, pins or clips very easilyand thus the cost of fitting a wear indicator 19 is very low.

The wear indicator 19 shown in FIGS. 2 and 3 is basically a linkcomprising a double-cranked plate 20 having an attachment hole 21 and ahairpin rod member 22 with a looped end 23 forming an attachment means.Cranked portions 24 of the plate 20 have holes 25 in them for receivingone end of the rod member 22 and therefore act as a device whereby thelink can be varied in length to conform to movement of the frictionassemblies. The link also includes a switch 26, comprising twocontacts27 and 28 held abutting each other by a spring clip 29 whose resilientend flanges 30 are apertured so the clip is held non-rotationally on therod member 22 which passes through the apertures. The contact 27 iscarried on, but insulated from, an end of the rod member 22 and thecontact 28 on, but insulated from, an end of a further rod member 31which passes through an aperture in an end flange 30 into holes on thecranked portions 24. Fitted onto the rod member 31 between the portions24 is a helical adjustable stop 35, which when compressed slides freelyon the rod member but when allowed to expand clamps itself to the rodmember. The spring clip 29 and the rod member 31 and the stop 35 providea device for sensing excessive variation of the length of the link inthat the stop 35 in cooperation with the portion 24 nearer the contactsacts as a lost motion device which is adjustable to the maximumpermissible wear and when this is ex ceeded the contacts 27 and 28 areseparated to provide a signal on terminals 36 signifying that the linkis of excessive length.

FIG. 4 shows in detail the mounting of the contacts 27 and 28. These arewelded to conductors 37 and are attached on insulating bodies 38 havingthrough axial bores in which the conductors extend. Holes 39 are drilledand tapped in these bodies through the conductors 37 for the terminals36 to be screwed in and make contact with the conductors 37. A boot-likeshroud 40 seats in grooves 41 in the bodies and protects the contactsagainst dirt. The ends of the insulating bodies to which the conductors37 do not extend have tapped holes 42 to receive the threaded ends ofthe rod members 22 and 31.

The design of the plate 20 is such that the distance between theportions 24 allows for the maximum range of permissible wear for a widerange of brakes and for the length necessary for the stop and itsmanipulation. The distance between the hole 21 and the nearer portion 24is preferably as large as possible since this distance is necessary notonly to allow the rod members to extend along it during normal usewithout the rod members freeing themselves from the holes 25 but also toallow the link to be used with differing brake diameters.

In the embodiment of FIG. the two wear indicators leads 48 and 49 areled into an insulating block 50 attached to a link 51 which can beattached to one of the brake shoes. The two leads 48 and 49 terminate incontact surfaces 52 and 53 which can be bridged by a contact 54 carriedby a piston-like block 55 of a resilient material such as hard rubber.The contact 54 is connected to this block by means of a knuckle jointformed by a ball 56 carried from the contact fitted into a sphericalbearing 57 in the block. The resiliency of the block can be modified byan annular slot 58 surrounding the spherical hearing. The block slidesin a piston-like man.- ner, in a cylindrical housing 59 connected to theblock 50, against the bias exerted by a weak elastomeric compressionspring 60 which also acts as a dirt-excluding seal. A wire coil springcould be used with or without a suitable internal or external seal. Theblock is displaceable in the housing by a rod 61 anchored in the blockand extending towards a lost motion device 62 whose other end is securedto the other brake shoe. The block is moulded around a bifurcated end 63of the rod or the rod otherwise connected to the block.

Whilst in the preferred embodiments illustrated, the indicator extendsbetween two friction assemblies it is apparent that a separate wearindicator could be used for each friction assembly, with the indicatorsattached between the friction assemblies and an anchorage on the torqueplate or a single wear indicator could be fitted to the frictionassembly more likely to wear and an anchorage on the backing plate.

Brake shoes of drum brakes follow a complex motion as wear proceedsdepending in part whether the wear is taken up by an adjuster or byincreasing the stroke of the actuator. It will be found that the wearindicator can be located so that it is not affected unduly by this. Ifthe design of brake is such that one or other end of the lining wearsmore than the other, it may be advisable totake this into considerationin the location of the wear indicator.

It is possible to arrange the spring clip 29 so that it fails when thecontacts are separated (or approached to each other). For example theclip could incorporate weak retaining springs engaging a peripheral ribon one or each contact (somewhat similarly to the springs in apress-stud) and relative movement of the contacts could snap theseretaining springs from the rib to disable the resiliency of the clip 29.Moreover insulating means could be sprung between the contacts.

The invention comprehends a construction consisting of two strips of aresilient plastics material each having a corrugation on one end, thetwo corrugations meshing and the contacting surfaces being metallizedand held together by a resilient clip. At least one of the strips wouldhave at least one corrugation which could be pulled out straight toprovide the lost motion before the two meshing corrugations were forcedto part and break contact between the metallization. In thisconstruction, there would be rubbing contact between the metallizationto keep the surface clean and the metallization would be wedged apartonly when all the lost motion had been utilized.

FIG. 6 shows a circuit for use with wear indicators of the typesillustrated in FIGS. 2 to 4 or FIG. 5 with normally closed pairs ofcontacts 27 and 28. A normally closed pair of contacts 27 and 28 isassociated with each brake and these are connected by a single conductorin series with each other, with a fuse 71 and with a heater coil 72 of athermal relay 73 across a battery 74 and an ignition switch 75. Alsoconnected across the battery and the ignition switch are an indicatorlamp 76 and contacts 77 of the thermal relay (these contacts beingclosed when the relay is cold). The lamp will be located in the cab ofthe vehicle.

On switching on the ignition for the vehicle, the indicator lamp glowsuntil the relay warms up and thus indicates the circuit is sound. If anyof the pairs of contacts opens or if the fuse fails, the heater is nolonger energized and the thermal relay trips so the lamp glows, the samehappens if a break occurs in the circuit.

It will be appreciated that the wear indicator denotes excessive lengthof a link interconnecting the friction assemblies and that an initialindication of excessive wear and need for adjustment will be givenduring brake actuation re-occurring during each actuation and anindication that the maximum account of adjustment has taken place willresult in a continuous signal. Thus if a brake is fitted with anadjustment need indicator and an amount of adjustment indicator, it ispossible to identify which indicator is open-circuited. With automaticadjusters, a signal re-occurring during each brake actuation indicates afaulty adjuster.

It will be appreciated that this circuit is easy to install and costsvery little.

For safety, it may be preferred to include a resistor or other currentlimiting device between points G and H.

Instead of using a thermal relay because it facilitates circuit testing,it is possible to use a conventional relay with normally closed contactswith a low impedance high current circuit element such as a vehiclestarter motor between the relay coil and earth and a connection betweenthe relay coil and the circuit element to supply the heavy current tothe element. The voltage drop across the element prevents any voltageacross the relay coil and so holds the contacts closed for testing.

The invention can be applied to disc brakes and an embodiment will nowbe described which is particularly suitable for disc brakes.

As can be seen most clearly from FIG. 8, a disc brake has two brake pads81 with linings 82 in a housing 83. These brake pads are arranged to beurged against opposite sides of a brake disc 85 hydraulically by a fluidintroduced by means of a connection 84 (FIG. 9) and the pads slide onpins 86. These pins are retained in the housing by means of clips 87 andhave associated with them anti-rattle springs 88, which minimizerattling of the pads 81 on the pins 86.

A cover plate 89 fits on top of an opening 90 in the housing 83 and isretained in place in the housing by means of clips 91 which engage onthe pins 86 outside the range of travel of the pads 81. This cover plateis accurately located by machined corners 92 in the opening 90. A limitswitch 94 is secured to the cover plate 90 by means of two screws 95(FIG. 9).

The limit switch is shown in greater detail in FIG. 10. It consists ofan insulating housing 97 into which two conductors 98 lead to form apair of fixed contacts one on each side of an insulating column 99. Themovable contacts of the limit switch are formed by the sides of aU-shaped member 100 which normally bear under their own resiliencyagainst the fixed contacts. The sides of this U-shaped member 100 arebent back along themselves to form a socket into which fit feelers 102which are of insulating material or as illustrated incorporateinsulating material 103. These feelers project out from the limit switchand are bent to pass through the cover plate 89 into the path of thepads 81. The ends of the feelers are spaced apart by a distance equal tothe thickness of the brake disc and normally twice the minimum thicknessof lining permissible and are symmetrically disposed about the centralplane of the brake disc. On the brake pads wearing, one or both padswill contact an end of a feeler 102 which will flex the respective sideof the U-shaped member 100 about the corner 105 at the base of theU-shape away from the respective fixed contact.

It will be apparent that the fixed contacts should not be normally incontact with the sides of the U-shaped member along the entire lengththereof but only in contact with a short length of the U-shaped memberat the free ends of the sides of this member. It is possible for thecolumn 99 to extend beyond the fixed contacts and to be used to locatethe U-shaped member. However, it is preferred that the U-shaped membershould have lugs projecting from its sides which can be bolted toanother part of the housing 97.

The limit switch shown in FIG. can be used for a range of disc brakes byadjustment of the feelers for example by bending them and by suitablyadapting the cover plate. The limit switch could be applied to drumbrakes by having the feelers engaging in holes in the brake shoes. Itwould also be possible to design the sides of the U-member to act in anover-center manner or to have an insulating resilient member forentering between contacts of a cooperating pair so that opening of acontact pair was not cancelled by release of the brake.

It will however be appreciated that other forms of the invention can beapplied to disc brakes for example an indicator could be bridged betweenthe brake pads.

The wear on a single pad could be sensed by using a single feeler and asuitably modified switch.

The circuit of FIG. 6 is applicable to the disc brake indicatorsillustrated in FIGS. 7 to 10. However modifications to this circuit canbe used to reduce the current consumed.

FIG. 11 illustrates three variations namely the use of an electronicrelay, the use of a capacitor as a delay, and the possible use of a testswitch.

The electronic relay comprises a resistor R12 in series with the wearindicators NB represented by a single contact pair. The voltage droppedacross this resistor R12 is fed through a diode D1 to a Darlington pairof transistors 0,, 0,; used to switch a lamp L. A capacitor C2 isconnected to the input of the Darlington pair, so that on initiallyswitching on the ignition switch 1 capacitor C2 charges and in chargingcauses transistors Q1 and Q2 to conduct thereby turning on the lamp.During charging of the capacitor C2 the charging current through thecapacitor C2 decays and in doing so turns off the Darlington pair, thelamp L being thereby extinguished. A diode D2 may be used to protect theDarlington pair against supply transients.

As an alternative to, or as an addition to, the delay provision providedby the diode D1 and the capacitor C2, a manually operable test switch,which may be incorporated in the hand brake I-IB, can be provided inseries with the other wear indicators. This test switch would beoperated to check the correct functioning of the circuit.

The embodiment of FIG. 12 illustrates a continuously self-monitoringsupervisory circuit. The voltage from the car battery is fed through theignition switch 1 across a bridge consisting of impedance R1 to R4. Thewear indicators NB are connected in series with a resistor R3 in one ofthe arms of the bridge. The output of the bridge is fed to the bases oftwo transistors Q1 and Q2 having a common emitter resistor R7 but havingseparate collector resistors R5 and R6. It will be appreciated that whenthe bridge is unbalanced by operation of one of the wear indicators, oneof the transistors Q1 and Q2 will be switched off or on depending on thebias and the circuit arrangement to feed a signal through a diode D3 orD4 to operate a Darlington pair of transistors Q3 and Q4. The wearindicators have a finite resistance when closed and are also disposed inthe respective arm relative to the resistor R3 in such a way that ashort circuit on one of the wear indicators causes the other of thetransistors Q1 and O2 to switch off the Darlington pair of transistorsQ3 and Q4. A capacitor C2 in series with a resistance R8 can be used toprovide an automatic warning (when the ignition is switched on) so thatthe system is checked for integrity of the lamp L.

Connected in series with the wear indicators can be one or more othersensors for supervising another element such as the clutch fluidreservoir, the gear box, the sump, the petrol tank, differential gearbox, the

brake fluid reservoir, and parts of the vehicle electrical system whichcan be supervised by electrical contacts.

I claim:

1. A vehicle brake lining wear indication system in and for a vehiclehaving a plurality of brakes, each having a movable lining carryingmember and an indicator, each indicator comprising at least one pair ofcontacts, means for biassing the pair of contacts together with thecontacts being separable by application of a force in opposition to thebias, and means whereby the pair of contacts is forced to separate inresponse to move- -ment of the lining carrying member during brakeactuation by more than a predetermined amount, the system comprising theindicators, a series circuit including the indicators, and a displaymeans associated with the series circuit and responsive to a breaktherein.

2. An indication system according to claim 1 for and in a vehicle inwhich at least some of the brakes comprise a rotor, a fixed part, and atleast two parts which carry the friction linings, and an actuator whichmoves said at least two parts when the brake is operated, at leastportions of two of the above-mentioned parts separating relative to eachother when the brake is operated, wherein the pair of contacts, thebiassing means, and the separating means of one indicator form a tieadapted to be fitted between said portions, in the separating meansthere being a lost motion device so arranged that on separation of saidportions the lost motion is taken up before the contacts are separated.

3. An indication system according to claim 2 for use when at least someof the brakes are drum brakes and wherein the relevant ties have lengthadjustment means.

4. An indication system according to claim 3 wherein each relevant tieincorporates a rod forming part of the lost motion device and the lengthadjustment means is a helical adjustable stop to limit the amount oflost motion and thus the length of the extended tie.

5. An indication system according to claim 1, wherein said at least onepair of contacts comprises two contacts which are permanently connectedto the series circuit and which are not relatively movable and abridging connection which provides complementary contacts to form twopairs of contacts, the bridging connection being carried in anarticulated manner and being subject to the biassing means.

6. An indication system according to claim 5, wherein the contacts arecontained in a housing, the bridging connection being carried by meansof a knuckle joint from a resilient block which is slidable in thehousing against the force exerted by the biassing means.

7. An indication system according to claim 1, wherein the at least onepair of contacts comprise a fixed contact and a movable contact, and thebiassing means comprises a resilient member on which the movable contactis provided, and the separating means comprises an insulated feeler.

8. An indication system according to claim 7, in and for a vehicle usingdisc brakes, each disc brake comprising a housing, at least oneactuator, a rotor, and opposed friction pads, the friction pads having adefined path of movement, comprising for each disc brake a switch bodycontaining the respective at least one pair of contacts and adapted tobe mounted on the housing, and the at least one insulated feeler havinga free end extending into the movement path whereby on abutment of theend with a friction pad the feeler is moved, the feeler being connectedwith one of said contacts to separate it from its complementary contact.

9. An indication system according to claim 8 wherein each switch bodycontains two fixed contacts each with its complementary movable contactand both movable contacts are provided on the same resilient memberwhich is U-shaped with one movable contact being on each leg thereof andeach leg being bent back on itself to form a socket, there being twofeelers each fitting into a respective one of said sockets.

10. An indication system according to claim 1 wherein also connected inthe series circuit are normally closed contacts of at least one otherindicator monitoring the condition of another element affecting vehiclesafety.

11. A system according to claim 1 wherein the display means comprises arelay which incorporates delay means whereby the relay does not operateimmediately on switching on the system but gives a false indicationthere is a fault in order to check the circuit.

12. A system according to claim 1 wherein the display means includes abridge circuit in one arm of which are located the contacts.

13. In and for a vehicle brake system having at least one brakeconsisting of a support, a rotor, at least one friction lining carryingmember, this member being mounted from the support, and an actuator formoving the member a sufficient distance for it to contact the rotor toachieve a brake actuation, which sufficient distance if it exceeds apreselected distance implies the need for at least adjustment of themember; an indicator comprising a pair of separable electrical contacts,means for resiliently biassing the contacts into engagement with eachother with the contacts being separable by application of a force inopposition to the bias, means responsive to movement of the member bymore than the preselected distance and arranged to move the contactsapart, and indicator means energized when the contacts are moved apart.

14. An indicator according to claim 13, wherein said responsive means isdisposed so that it is abutted by the member when the preselecteddistance is exceeded.

15. An indicator according to claim 13 wherein said responsive means isconnected to the member by a lost motion device.

1. A vehicle brake lining wear indication system in and for a vehiclehaving a plurality of brakes, each having a movable lining carryingmember and an indicator, each indicator comprising at least one pair ofcontacts, means for biassing the pair of contacts together with thecontacts being separable by application of a force in opposition to thebias, and means whereby the pair of contacts is forced to separate inresponse to movement of the lining carrying member during brakeactuation by more than a predetermined amount, the system comprising theindicators, a series circuit including the indicators, and a displaymeans associated with the series circuit and responsive to a breaktherein.
 2. An indication system according to claim 1 for and in avehicle in which at least some of the brakes comprise a rotor, a fixedpart, and at least two parts which carry the friction linings, and anactuator which moves said at least two parts when the brake is operated,at least portions of two of the above-mentioned parts separatingrelative to each other when the brake is operated, wherein the pair ofcontacts, the biassing means, and the separating means of one indicatorform a tie adapted to be fitted between said portions, in the separatingmeans there being a lost motion device so arranged that on separation ofsaid portions the lost motion is taken up before the contacts areseparated.
 3. An indication system according to claim 2 for use when atleast some of the brakes are drum brakes and wherein the relevant tieshave length adjustment means.
 4. An indication system according to claim3 wherein each relevant tie incorporates a rod forming part of the lostmotion device and the length adjustment means is a helical adjustablestop to limit the amount of lost motion and thus the length of theextended tie.
 5. An indication system according to claim 1, wherein saidat least one pair of contacts comprises two contacts which arepermanently connected to the series circuit and which are not relativelymovable and a bridging connection which provides complementary contactsto form two pairs of contacts, the bridging connection being carried inan articulated manner and being subject to the biassing means.
 6. Anindication system according to claim 5, wherein the contacts arecontained in a housing, the bridging connection being carried by meansof a knuckle joint from a resilient block which is slidable in thehousing against the force exerted by the biassing means.
 7. Anindication system according to claim 1, wherein the at least one pair ofcontacts comprise a fixed contact and a movable contact, and thebiassing means comprises a resilient member on which the movable contactis provided, and the separating means comprises an insulated feeler. 8.An indication system according to claim 7, in and for a vehicle usingdisc brakes, each disc brake comprising a housing, at least oneactuator, a rotor, and opposed friction pads, the friction pads having adefined path of movement, comprising for each disc brake a switch bodycontaining the respective at least one pair of contacts and adapted tobe mounted on the housing, and the at least one insulated feeler havinga free end extending into the movement path whereby on abutment of theend with a friction pad the feeler is moved, the feeler being connectedwith one of said contacts to separate it from its complementary contact.9. An indication system according to claim 8 wherein each switch bodycontains two fixed contacts each with its complementary movable contactand both movable contacts are provided on the same resilient memberwhich is U-shaped with one movable contact being on each leg thereof andeach leg being bent back on itself to form a socket, there being twofeelers each fitting into a respective one of said socketS.
 10. Anindication system according to claim 1 wherein also connected in theseries circuit are normally closed contacts of at least one otherindicator monitoring the condition of another element affecting vehiclesafety.
 11. A system according to claim 1 wherein the display meanscomprises a relay which incorporates delay means whereby the relay doesnot operate immediately on switching on the system but gives a falseindication there is a fault in order to check the circuit.
 12. A systemaccording to claim 1 wherein the display means includes a bridge circuitin one arm of which are located the contacts.
 13. In and for a vehiclebrake system having at least one brake consisting of a support, a rotor,at least one friction lining carrying member, this member being mountedfrom the support, and an actuator for moving the member a sufficientdistance for it to contact the rotor to achieve a brake actuation, whichsufficient distance if it exceeds a preselected distance implies theneed for at least adjustment of the member; an indicator comprising apair of separable electrical contacts, means for resiliently biassingthe contacts into engagement with each other with the contacts beingseparable by application of a force in opposition to the bias, meansresponsive to movement of the member by more than the preselecteddistance and arranged to move the contacts apart, and indicator meansenergized when the contacts are moved apart.
 14. An indicator accordingto claim 13, wherein said responsive means is disposed so that it isabutted by the member when the preselected distance is exceeded.
 15. Anindicator according to claim 13 wherein said responsive means isconnected to the member by a lost motion device.